1. Field of the Invention
The present invention relates to an apparatus and method for processing signal. More specifically, it relates to an apparatus and method for processing a digital image signal or the like to reduce an influence of noise from the digital image signal or the like.
2. Description of Related Art
As a signal processing apparatus for processing a digital image signal, for example, a signal processing apparatus for reducing an influence of noise from a digital image signal, a circulation-type noise-reducing device in which a field memory or a frame memory is used has been employed.
This type of noise-reducing device performs motion compensation by use of a motion vector on an image signal of previous frame that is stored in the frame memory, extracts a noise component from a difference between the image signal of previous frame as motion-compensated and an image signal of a current frame, and subtracts this extracted noise component from the image signal of current frame, thereby reducing noise.
In such the noise-reducing device, however, a motion vector must be detected between one frame and another, thus making a movement distance thereof larger than that of a case where a motion vector is detected between one field and another. Therefore, a search extent needs to be larger, thus increasing a circuit size.
Further, in another noise reducing device, a motion vector is detected between one field and another instead of thus inter-frame motion vector detection. Motion compensation is performed on an image signal of previous field using this detected motion vector. By extracting a noise component from a difference between an image signal of the previous field as motion-compensated and an image signal of a current field and subtracting this extracted noise component from the image signal of current field, noise is reduced.
According to the noise reducing device, however, there is a case where an influence of noise may have a vertical spread in s signal level. Further, the signal level fluctuates at the boundary may cause flickering display to occur.